Coplanar silicon/aluminum resonators with internal quality factor above 2M: fabrication^*

Extremely low intrinsic loss coplanar resonators are critical elements in superconducting quantum computing devices, photon detectors, parametric amplifiers and quantum memories. Here we describe the fabrication and measurement of superconducting coplanar waveguide microwave resonators on silicon substrates with internal quality factors over 2 millions at low powers, corresponding to single-photon regime. These quality factors are achieved by careful optimization of resonators geometry, measurement setup and key TLS-containing interfaces: metal-air, metal-substrate, and substrate-air. We provide a detailed analysis of the design and technological factors impact on resonators quality, including multi-step substrates cleaning, aluminum films crystalline structure, low-damage dry etching, design features and air-bridges application. Finally, using the same process flow we fabricate and characterize superconducting tunable X-mon qubits with the coherence over 100 us, confirming well-known correlations between resonators and qubits quality.

*Devices were fabricated at the BMSTU Nanofabrication Facility (Functional Micro/Nanosystems, FMNS REC, ID 74300).